Congressman John Conyers, the chair of the House Judiciary Committee (which includes the Immigration Subcommittee) was angered by the leak and fired off this letter to DHS Secretary Chertoff:

Dear Mr. Chertoff:

I was startled to read in today's Associated Press that a "federal law
enforcement official" has leaked information about an immigration case
involving a relative of Senator Obama. Even more troubling, the AP
reports that it could not "could not establish whether anyone at a
political level in the Bush administration or in the McCain campaign
had been involved," a very disturbing suggesting indeed. This leak is
deplorable and I urge you to take immediate action to investigate and
discipline those responsible.

I note that this is not the first leak of law enforcement information
apparently designed to influence the coming Presidential election -- in
recent weeks law enforcement sources leaked information about an
alleged investigation of a community services organization, a leak that
the Department of Justice informs me is now under investigation by the
Department's Office of the Inspector General and Professional
Responsibility.

Such leaks are deeply harmful to the political process, and the
American people expect and deserve better from their government and its
law enforcement agencies.